The use of combination locks, such as padlocks, is well known and it is particularly desirable to have a lock which an operator can change the combination code when they wish to. An example of such a combination lock is disclosed in our earlier European patent application published under the number EP1837466. The combination lock disclosed therein uses clutch wheels, associated with each dial, to allow the combination to be changed. In a code change condition the clutch wheels are fixed and the dials can be moved over the clutch wheels so that a new code becomes associated with the unlocking position for the padlock. However, in order to ensure that the padlock does not become accidentally recoded it is necessary that the force required to move the dials relative to the clutch wheels is quite high and it is therefore necessary to use a tool to apply sufficient force to the dial. Although the tool required is simply a small rod, the rod supplied with the padlock or another suitable tool may not be conveniently available when the operator wishes to change the code.
In order to ensure correct alignment of the clutch wheel and dial the external surface of the former and internal surface of the latter are provided with a series of ridges and associated grooves, one for each number on the dial, which should be aligned with each other. However, it is possible, in principle, for the ridges and grooves to be incorrectly aligned when the dials are recoded. In this instance when an operator comes to try and unlock the padlock using the code they had intended the padlock will not unlock.